Heroin users appear to run a higher risk of dying if they abstain from taking the drug for a few months then resume shooting up. Experts say the finding, reported in the current issue of The Lancet, should spur close monitoring of individuals after they are released from detox programs.

Despite decades of study, the most dangerous factors in heroin overdose are not well known: Fatal dosage levels vary, and descriptions of the victims' lifestyles are often sketchy. To obtain a clearer picture how heroin usage can lead to death, forensic scientists Franco Tagliaro, Zeno De Battisti, and Mario Marigo of the University of Verona, Italy, and Frederick Smith of the University of Alabama, Birmingham, went back in time by examining the hair of overdose victims. Tiny amounts of morphine, the addictive component of heroin, are woven into the protein scaffolding of hair, says Tagliaro. Thus hair provides a permanent record of the heroin dosage over time--depending on a user's hair length--from months to years.

The investigators measured morphine levels in hair from 37 overdose victims, comparing them to hair from 37 active heroin addicts and 37 former addicts, who were mostly heroin-free for several months. Average morphine levels were five times lower in the victims' hair than in the active addicts' hair, and about the same as the former addicts' hair--suggesting that the victims largely abstained from heroin before taking their fatal dose. Since all the hair sampled was about 4 centimeters long, and hair grows about 1 centimeter per month, Tagliaro suspects that the victims must have taken little heroin for at least 4 months.

The findings bear out suspicions that users who abstain and then take up the habit often die from overdose, says Tagliaro. The study is also "very valuable" in that it underscores the need to educate recovering addicts, says Werner Baumgartner, chairman of Psychemedics Corporation in Culver City, California, who invented the hair analysis technique in 1978 to investigate drug use history. "Hair analysis," says Baumgartner, shows that "people don't realize the dangers of lowered heroin tolerance."